1 Scientific RepoRts | 6:31885 | DOI: 10.1038/srep31885 www.nature.com/scientificreports Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide shakhawan Al-Zangana 1 , Maria Iliut 2 , Gökçen Boran 1,3 , Michael turner 4 , Aravind Vijayaraghavan 2 & Ingo Dierking 1 Graphene oxide (GO) lakes of diferent sizes were prepared and dispersed in isotropic and nematic (anisotropic) luid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25–60 o C) and frequency range (100 Hz–2 MHz). The mixtures containing GO lakes exhibited varying dielectric relaxation processes, depending on the size of the lakes and the elastic properties of the dispersant luid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO lakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO lakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO lakes in the isotropic solvent was increased. Polarizing microscopy showed that GO lakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB. Due to their outstanding physical and chemical features, graphene research and that of other two-dimensional materials, including oxides, have recently exhibited much interest 1–4 . his was only made possible when the chal- lenge to produce monolayer graphene was solved through mechanical exfoliation by Novoselov et al. 5 . Graphene oxide (GO) is a one- or very few-atomic-layer thick material, produced by the mechanical exfoliation of graphite oxide, yielding sheets decorated with hydroxyl and epoxide functional groups on the surface and carbonyl and carboxyl groups at the edges 6,7 . his makes the electrical conductivity of GO much smaller as compared to that of graphene 8 and provides a very high dielectric permitivity 9 . Due to the hydrophilic nature of GO, molecules of polar solvents easily intercalate into the GO layers 10 . he self-assembly of GO lakes in isotropic media (oten water) has been found to result in a lyotropic nematic liq- uid crystal when the concentration of the GO exceeded approximately 1 mg/mL 6,7,11–13 . he formation of this phase depends on the polarity of the medium and the size of the GO lakes. Due to its high polarity, water has been shown to be an ideal solvent for the formation of stable GO dispersions and facilitating lyotropic nematic mesomorphism. On the other hand, the electro-optic response of a thermotropic nematic liquid crystal has been shown to be improved through doping with GO 14 . he coupling of any electrical dipoles on the surface of the GO lakes with the electrical dipoles of the mesogen and the trapping of the always present ionic contamination by GO lakes could be the main reason behind the dielectric gain and the improved electro-optic behaviour of liquid crystal-GO dispersions. he nematic is the most common and the simplest of the liquid crystalline phases, the one with the highest symmetry. Molecules possess long-range orientational order, but no positional order of their centres of mass, with the long axis of the molecules aligning roughly along an average direction, called the director n 15 . he com- mon uniaxial nematic phase has two characteristic molecular dielectric relaxation processes; the high frequency 1 School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom. 2 School of Materials and National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom. 3 Physics Department, Bogazici University, Istanbul, 34342, Turkey. 4 School of chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom. Correspondence and requests for materials should be addressed to I.D. (email: Ingo.Dierking@manchester.ac.uk) received: 10 June 2016 accepted: 29 July 2016 Published: 24 August 2016 opeN